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Biomedical subjects

J D Andrade

Publications and source records attributed to J D Andrade.

At least 37 records · Page 2Linked to original sources
PubMed1988

On-line sensors for coagulation proteins: concept and progress report.

The assessment of blood damage and of the activation of the coagulation, complement and/or inflammatory systems by cardiovascular and extracorporeal devices is difficult at best. Immunoassay methods are now available for the measurement of many of the proteins, enzymes and peptides involved in coagulation, thrombosis, complement and inflammation. We present a long-range project and plan to develop an array of remote, on-line, semicontinuous immunosensors for selected coagulation proteins, based on fluoroimmunoassay principles. The free/bound separation step is performed optically. Excitation of fluorescence is performed via an evanescent wave produced by total internal reflection and waveguide optics. Fluorescence emission is collected only in the near field. Means to deliver fluorescently-labelled reagent and to modify the antigen-antibody binding constant are presented and discussed. The results of non-specific binding, plasma-blood fluorescence, and blood compatibility are also discussed.

Biocompatible Materials↗
PubMed1988

Scanning tunnelling microscopic images of amino acids.

We present images of amino acids adsorbed on highly orientated pyrolytic graphite (HOPG) obtained with the scanning tunnelling microscope (STM) in air. Individual molecules can be observed although the majority of adsorbates appear to form clusters. In the case of leucine, methionine, and tryptophan, two molecules often associate together to form a dimer. Single or dimer glycine molecules were not seen, but a cluster of a number of them was observed. The various adsorbed states may be related to the different interactions between the amino acids and the graphite surface. The mechanism of image formation of the amino acids is probably related to charge transfer mechanisms.

Adsorption↗
PubMed1987

Adsorption of low density lipoproteins onto selected biomedical polymers.

This study examines the interaction of human low density lipoprotein (LDL) with a select group of biomedical polymers. The adsorption characteristics of LDL on cured filler-free poly(dimethyl Siloxane) (C-PDMS), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxyethyl methacrylate) (PHEMA) and glass are presented. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within one minute (0.19 +/- 0.01 ug/cm2). Adsorption of LDL to polymer surfaces appeared to be dependent upon both the polymer hydrophobicity (or apolar nature), and flexibility (or dynamic nature) at the interface. Increased surface concentrations were observed for Biomer (0.32 +/- 0.01 ug/cm2) as well as other polymers which exhibited both hydrophobic and elastomeric properties. Temperature changes between 25 degrees C and 37 degrees C were found to significantly influence the surface concentration of LDL on Biomer (0.16 +/- 0.01 ug/cm2 at 25 degrees C versus 0.32 +/- 0.01 ug/cm2 at 37 degrees C). A lipid core phase transition at 36 degrees C was believed to be responsible for the temperature influence. Preliminary competitive adsorption studies of LDL with albumin (HSA) and serum on silicone surfaces suggests that LDL adsorption occurred rapidly and preferentially (0.25 +/- 0.01 ug/cm2 for LDL alone; 0.33 +/- 0.01 ug/cm2 for LDL + HSA; 0.15 +/- 0.01 ug/cm2 LDL + serum). Preliminary studies on the role of LDL in calcification were not conclusive. It can be concluded that LDL adsorption is dependent upon polymer hydrophobicity, flexibility and temperature. Competitive adsorption experiments suggests that LDL may have a substantial influence on protein adsorption.

Adsorption↗
PubMed1987

Plasma protein adsorption: the big twelve.

We have discussed the general principles of protein adsorption at solid-liquid interfaces from single component and multicomponent solutions, based on qualitative kinetic models that include mass transport considerations, initial interaction energies, surface-dependent conformational changes, and possible desorption processes. We have surveyed plasma protein components greater than one milligram per milliliter in concentration, which we call "The Big Twelve." We considered their size, concentration, diffusion coefficient, structure and function, and methods of estimating their "surface denaturability" by using bulk solution measures of denaturation and conformational change. We have suggested that the role of the carbohydrate moieties in plasma proteins may have some bearing on their adsorption properties. We further suggest that lipoproteins, because of their lipid phase transition and conformational lability at body temperature, may tend to dominate the adsorption process, particularly on mobile elastomeric polymer surfaces. We suggest that detailed consideration of the structure and characteristics of each of the proteins involved is necessary in order to begin to understand plasma adsorption processes. Detailed characterization and understanding of the solid surface in the aqueous and protein environments are also required.

Adsorption↗
PubMed1986

Human haptoglobin adsorption by a total internal reflection fluorescence method.

Haptoglobin (Hp) is one of the major protein constituents of plasma. Three different forms are found in the population. The 1-1 and 2-2 forms adsorb similarly onto hydrophobic silica [treated with dimethyl dichlorosilane (DDS)] and onto clean silica, although the affinities on the silica surface are lower at 60 minutes contact time. The two forms desorb differently from silica, but desorb similarly from DDS-silica. Adsorption is less reversible on the hydrophobic surface. Due to its adsorbtion tendencies and its high concentration in plasma, the adsorption of Hp may be important in blood interaction at solid-liquid interfaces.

Adsorption↗
PubMed1985

Immunochemical detection by specific antibody to thrombin of prothrombin conformational changes upon adsorption to artificial surfaces.

Polyclonal antihuman alpha-thrombin antibodies produced in rabbits reacted minimally (less than 0.05%) in solution with human prothrombin. However, when prothrombin was adsorbed to artificial surfaces such as polyvinyl chloride (PVC), the cross-reactivity of surface-bound prothrombin with antibody IgG to thrombin (greater than 95% purity) was shown to be significantly enhanced. On PVC, the molar ratios of antibody IgG to thrombin/prothrombin approached the same level as that of antibody IgG to thrombin/thrombin when thrombin was adsorbed to the same material. The analyses of antigen-antibodies interaction, in solution with a direct binding assay by immune precipitation at high-speed centrifugation (160,000 g, 30 min), and on solid-phase PVC, were accomplished by use of double-labeling technique, i.e., 131I-thrombin (or 131I-prothrombin) and 125I-antibody IgG to thrombin. The results appear to suggest that prothrombin adsorption to PVC has resulted in some molecular conformational changes so that immunologically the adsorbed prothrombin resembles that of adsorbed thrombin on the same PVC surface.

Adsorption↗
PubMed1985

Oxy- and deoxyhaemoglobin adsorption onto glass and polymer surfaces.

The adsorption of deoxyhaemoglobin (deoxyHb) and oxyhaemoglobin (oxyHb) was determined on clean glass, n-pentyl triethoxysilane (NPS)-treated glass, polystyrene (PS), and a polyetherurethane (PEU). The adsorbed amounts range from 0.1 to 0.6 micrograms/cm2 for oxyHb and from 0.3 to 0.7 micrograms/cm2 for deoxyHb. DeoxyHb adsorbs onto all these surfaces more than oxyHb. The more hydrophobic the surface, the more adsorption of both deoxy and oxyHb forms. These results suggest the oxyHb and deoxyHb interact differently with the surfaces studied. It is likely that the surface hydrophobicity of Hb plays a major role in Hb adsorption onto surfaces; the deoxyHb surface is more hydrophobic than the oxyHb surface. The binding sites for Hb adsorption may include the clefts between alpha 1, beta 1. A surface-induced dimerization mechanism is proposed to explain the adsorption of oxyHb.

Adsorption↗
PubMed1983

Surface modification and evaluation of some commonly used catheter materials. I. Surface properties.

Double catheter systems consisting of a stiff outer catheter and a flexible, buoyant, flow-directed, inner catheter which is often balloon-tipped have been employed with increasing frequency recently in both therapeutic and diagnostic procedures. Their use, however, has been restricted because of the excessive friction generated between the two catheters. In an attempt to decrease friction between polymers commonly used as catheter materials, oxidation of polyethylene, fluorinated ethylene-propylene copolymer, poly(vinyl chloride), silicone rubber, and polystyrene surfaces was induced by exposing the polymers to radio frequency glow discharge (RFGD) in a helium environment. All polymers were surface characterized utilizing x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurements before and after oxidation. This article describes the materials and methods used to fabricate and characterize the polymer surfaces and the results of the characterization. The results indicate that increases in oxygen concentration at the surface of the polymers and decreases in air-water contact angles occur with increased RFGD exposure time. Plateau values were usually obtained after 5-30 s exposure time, yet no apparent changes in surface topography were noted by scanning electron microscopy. The hydrophilic surfaces produced were stable for up to three months storage time in air.

Biocompatible Materials↗
PubMed1983

Surface modification and characterization of some commonly used catheter materials. II. Friction characterization.

The effects of the modification of polystyrene (PS), polyethylene (PE), poly(vinyl chloride) (PVC), silicone rubber (SR), and fluorinated ethylene propylene (FEP) copolymer by radio frequency glow discharge in a helium environment were presented in part I. The hydrated polymer surfaces were characterized by XPS, SEM, visual microscopy, and by contact angle measurements. In general, exposure of the polymers to RFGD produced an oxidized hydrophilic surface, yet the roughness of the surface was unaltered by the relatively mild plasma conditions used. In this article, the frictional behavior of oxidized and unoxidized SR, PE, and FEP in distilled water, isotonic saline, and blood plasma environments is examined experimentally. The results are discussed in relation to the properties generally believed to affect frictional phenomena and to the surface properties as determined in part I. Results indicate that RFGD-treated SR generates less friction than untreated SR when dragged across all untreated and treated polymer surfaces, whether the medium is distilled water or an isotonic saline solution. Friction is consistently lower in a blood plasma medium between all surfaces investigated, most probably because of the presence of adsorbed proteins at the polymer interfaces.

Biocompatible Materials↗
PubMed1983

Minimizing the aggregation of neutral insulin solutions.

Various solution additives affect the solubility and macroaggregation of insulin in buffered aqueous solutions at physiological pH. The solubility of insulin may be improved with the addition of small amounts of aspartic acid, glutamic acid, EDTA (ethylenediaminetetraacetic acid), lysine, Tris buffer, or bicarbonate buffer. In addition, the propensity of dissolved insulin to reaggregate and precipitate may be inhibited by such additives. Buffered physiological (pH 7.4) saline solutions containing 0.001-0.003 M lysine in the presence of 0.005 M EDTA or 0.01 M lysine in the absence of EDTA improve insulin solubility and are effective in minimizing aggregation. Solutions thus prepared may be suitable for application in intravenous insulin infusion devices and may be useful commercial insulin preparations.

Chemical Precipitation↗
PubMed1982

Blood-materials interactions: the minimum interfacial free energy and the optimum polar/apolar ratio hypotheses.

Numerous hypotheses exist to explain observed blood-materials interactions. It is the purpose of this article to test two popular hypotheses, namely, the minimum interfacial free energy hypothesis and the optimum polar/apolar ratio hypothesis. Methacrylate polymers and copolymers were characterized using the captive bubble underwater contact angle method; bulk water content was determined by gravimetric methods; streaming potential measurements were made; and surface roughness and possible particulate contamination were evaluated by reflected light microscopy. In vitro blood tests include whole blood clotting time measurements on polymer-coated tubes; centrifugal force platelet adhesion on polymer-coated coverslips; and a measure of the partial thromboplastin time, Russell's viper venom time (Stypven time), and the prothrombin time of native whole blood exposed to polymer-coated microscope slides. Results suggest that platelet adhesion correlates in the opposite direction of whole blood clotting time and partial thromboplastin time, emphasizing the need for a multiparameter approach to blood-materials testing. Based on these tests the minimum interfacial free energy hypothesis is not supported. In fact, the data suggest the opposite to be true. It is apparent that platelet adhesion can be a misleading indicator of blood compatibility. Neither hypothesis can explain the apparent conflict between the platelet adhesion data and the coagulation time data.

Animals↗
PubMed1981

The effects of radioiodination and fluorescent labelling on albumin.

The preparation and characterization of fluorescamine -, fluorescein isothiocyanate (FITC) -, and radioiodine-labelled bovine serum albumin is critically evaluated. Electrophoretic mobility and ion-exchange chromatography, together with measures of degree of conjugation and sulfhydryl content, are used to assess the changes due to conjugation. Fluorescamine labelling results in drastic changes in chromatographic behavior and electrophoretic mobility. FITC labelling also results in significant changes in chromatographic and electrophoretic properties. Radioiodination leads to minor changes in chromatographic properties and oxydation of sulfhydryl groups, with little or no change in electrophoretic properties. All three labels have some degree of lability and show increased levels of free label with time, even after extensive initial purification. It is concluded that the two fluorescent labels and possibly the radioiodine labelling method used here are unsuitable for certain studies of BSA, such as its adsorption at solid-liquid interfaces.

Chemical Phenomena↗
PubMed1980

An analysis of the heterogeneity of albumin.

A simple and rapid procedure for characterization of serum albumin samples and for the isolation of fractions from fresh serum or commercial sources has been developed, based on DEAE Sepharose CL-6B ion exchange chromatography. Characterization of the fractions included sulfhydryl analysis, gel electrophoresis, and immunoelectrophoresis. Both analytical and preparative procedures were used. It has been shown that the relative content of the fractions varies from individual to individual. It has also been shown that certain fractions found in commercial preparations are artifacts which should be removed before performing serious studies with serum albumin.

Animals↗